Field of the Invention
The present invention relates to a magnetic-disk glass substrate, a magnetic disk and a method for manufacturing a magnetic-disk glass substrate.
Background Information
Nowadays, personal computers, digital versatile disc (DVD) recorders, and the like have a built-in hard disk drive (HDD) for data recording. In particular, a magnetic disk in which a magnetic layer is provided on a glass substrate is used in a hard disk drive that is used in a device premised on portability, such as a notebook-type personal computer, and magnetic recording information is recorded on or read from the magnetic layer with a magnetic head that flies slightly above the surface of the magnetic disk. A glass substrate is unlikely to be plastically deformed compared with a metal substrate (aluminum substrate) and the like, and thus is preferably used as a substrate of the magnetic disk.
Moreover, the density of magnetic recording has been increased to meet the demand for an increase in the storage capacity of hard disk drives. For example, the magnetic recording information area (recording bit) has been made smaller using a perpendicular magnetic recording system that causes the direction of magnetization in the magnetic layer to be perpendicular to the surface of the substrate. This makes it possible to increase the storage capacity per disk substrate. Also, in order to further increase the storage capacity, the distance between the recording and reproducing element and the magnetic recording layer is made very short by causing the element of the magnetic head to project farther, thus further improving the accuracy of the recording and reproducing of information (improve the S/N ratio). It should be noted that such control of the recording and reproducing element of the magnetic head is called a dynamic flying height (DFH) control mechanism and a magnetic head equipped with this control mechanism is called a DFH head. A magnetic-disk glass substrate that is used in an HDD in combination with such a DFH head is produced so as to have an extremely smooth main surface in order to prevent the substrate from colliding or coming into contact with the magnetic head and the recording and reproducing element that projects farther therefrom.
A magnetic-disk glass substrate includes a pair of main surfaces, side wall surfaces, and chamfered surfaces between the main surfaces and the side wall surfaces. Conventionally, it has been known that it is possible to prevent the generation of particles due to rubbing against a spindle inside an HDD and to suppress problems such as head crash and thermal asperity by forming the side wall surfaces and/or the chamfered surfaces of the magnetic-disk substrate to have surface roughness that is smaller than or equal to a predetermined value or by forming the side wall surfaces and/or the chamfered surfaces to have a desired shape. For example, JP 2006-236561A states that the side wall surfaces and the chamfered surfaces are formed to have surface roughness of 1 μm or less in Rmax, and that a curved surface having a radius of 0.003 mm or more to less than 0.2 mm is interposed at least one of between the side wall surfaces and chamfered surfaces of the glass substrate and between the main surfaces and chamfered surfaces of the glass substrate.